Crystal-field interpretation of the temperature dependence of the57Fe Mössbauer quadrupole splitting in two orthopyroxenes

The temperature dependences of the M2 and the M1 ferrous quadrupole splittings in two orthopyroxenes have been studied. The valence contributions to the EFG were calculated from the Boltzmann averages of the expectation values of the EFG components over the corresponding⁵D levels, while the lattice contributions were obtained from lattice summations. The proper⁵D level schemes were each determined by diagonalization of the full crystal-field Hamiltonian, for which the operator coefficients were calculated so as to take into account the real C₁ symmetry of the FeO ₆ ^10– clusters. The calculations were based on the lattice and the charge data related to ferrosilite.